CA1337069C - Process for removal of sulphur compounds and nitrogen peroxide from fluid streams - Google Patents

Abstract

This invention provides a method for removing sulphur compounds from a fluid stream and decomposing such compounds to produce sulphur. Sour natural gas can be sweetened effectively by this invention, and sulphur can be prepared thereby. The invention employs a catalyst that is capable of providing reactive oxygen. The catalyst is preferably formed by impregnating alkali metal sulfide and sulfides(s) or selenide(s) of metal(s) showing polyvalent and/or amphoteric character, e.g. Zn, etc. on a microporous type support (e.g., alumina). Its activity is sustained by exposure to sulphur dioxide or nitrogen peroxide and the like. A method is also described by which sulphur dioxide may be absorbed from flue gas and converted to sulphur.

Description

PROCESS FOR REMOVAL OF SULPHUR COMPOUNDS
AND NITROGEN PEROXIDE FROM FLUID STREAM

Field of Invention The desirability of identifying an effective means for 05 removing sulphur compounds from fluid streams will be readily appreciated. This invention comprises a novel method and catalyst for effecting such removal and the subsequent treatment of such sulphur compounds to produce elemental sulphur. More particularly this invention is applicable to the removal of hydrogen sulphide and other sulphur compounds from sour natural gas, and other fluid streams, and the conversion of the sulphur therein to elemental sulphur.
By the same process applied in a different order, the invention may be used to remove certain oxygen compounds from gas streams, and particularly to remove sulphur dioxide, nitrogen peroxide and carbon dioxide from flue gases.
Background of the Invention Sulphur compounds are often considered to be undesirable compounds in gas mixtures and other fluid streams.
The most common example of this is that of natural gas containing hydrogen sulphide. Natural gas may also contain as undesirable sulphur compounds, quantities of carbonyl sulphide, carbon disulphide, mono and dialkyl sulphides, alkyl-type disulphides and thiophenes.

1 3~7069 _ - 2 -The removal of such sulphur-containing compounds from gas streams has been addressed by a number of methods in the past. These methods generally rely on direct reactions with the sulphur compounds, or proceed to first separate the sulphur compounds from the gas stream by an absorption stage.
05 In the latter case, the sulphur and other constituent elements of the absorbed compounds must then be extracted, if the absorptive medium is to be regenerated. A particularly desirable regenerative process would be one which produces elemental sulphur from the same reaction bed.
Various systems have been explored with the view of removing hydrogen sulphide from gas streams and producing elemental sulphur. The Claus process, as currently applied, is a complex multi-stage system involving the absorption of the hydrogen sulphide in an amine absorbent, flashing of H2S
from the amine, followed by the burning of part of the hydrogen sulphide to sulfur dioxide, and subsequently reacting the hydrogen sulphide with the sulfur dioxide to produce sulphur as the final product as elemental sulphur.
It would be obviously desirable to provide a method for removal of hydrogen sulphide and other sulphur containing compounds from a fluid stream at ambient temperatures followed by the subsequent conversion at moderate temperatures of the sulphur compounds into elemental sulphur and other decomposition products.
Flue gases generally contain a mixture of sulphur dioxide, nitrogen peroxide and carbon dioxide. It would be . ,.

1 337~69 desireable to have a process which effectively removes such compounds from flue gas, and allows for their separation and subsequent disposition.
Objects of the Invention 05 It is therefore an object of the invention to remove sulphur compounds from a fluid stream and recover elemental sulphur therefrom. It is further an object to do so in the same reaction bed.
It is also an object of the invention to provide a means which will allow removal and decomposition of hydrogen sulphide from a gas stream, and the separation of the sulphur so produced, at a modestly elevated temperature (circa 250C - 600C).
A further object of the invention is to remove sulphur dioxide, nitrogen peroxide and carbon dioxide, separately or collectively from a gas stream, and then to convert the sulphur dioxide to sulphur, convert the nitrogen perioxide to nitric oxide, and separately release the carbon dioxide, nitric oxide and sulphur so produced.
These and other objects of the invention will become apparent from the description of the invention and claims thereto which follow.
summarY of the Invention This invention comprises a specially prepared bed for absorbing hydrogen sulphide or sulphur dioxide from a fluid stream and subsequently decomposing it into elemental sulphur.

This same bed may be used to absorb nitrogen peroxide and carbon dioxide from a gas stream for subsequent separate recovery.
A suitable bed for treating hydrogen sulphide or sulphur dioxide comprises a microporous support adapted to 05 accommodate or absorb hydrogen sulphide or sulphur dioxide therein, which support contains an alkali metal sulphide or selenide together with a sulphide or sulphides, (or selenide/s) of metals showing polyvalent and/or amphoteric character deposited therein, and is thereby capable of providing "reactive oxygen", e.g. having peroxide-like characteristics after exposure to a source of oxygen.
The use of "and/or" in the above discussion, and throughout this disclosure, is to be taken in its non-exclusory sense. Thus, a mixture of both amphoteric and polyvalent compounds may be used in place of either alone, and a metal which is both amphoteric and polyvalent is intended to be included by this expression.
The reference to "reactive oxygen" is intended to refer to oxygen in an elevated energy state whereby the oxygen is available to react with the non-sulphur component of the compounds being treated so as to release sulphur.
Amphoteric metals are those metals which show a capacity to react both with acids and bases.
A bed so prepared, according to this invention is also adapted to remove and decompose carbonyl sulphide, carbon disulphide, mono and dialkyl sulphides, alkyl-type disulphides, and thiophenes from a gas or liquid stream by contacting such a X stream with the aforesaid bed.

1 33:7069 This same bed is capable of absorbing oxygen-cont~;n;ng compounds to provide reactive oxygen. Suitable compounds for this effect are sulphur dioxide and nitrogen peroxide.
05 Examples of amphoteric or polyvalent metal sulphides or selenides suitable for use in this invention include, amongst others, sulphides or selenides of metals from the group consisting of zinc, manganese, iron, copper, cobalt, aluminum, vanadium, molybdenum, tin and nickel as well as mixtures thereof. Examples of alkali metals suitable for use in this invention include lithium, potassium, sodium, cesium and rubidium, as well as mixtures thereof.
One method of preparing the bed is by:
(a) preparing in aqueous solution a mixture of an alkali metal salt and a polyvalent and/or amphoteric metal salt;
(b) impregnating a support with the mixture described in (a) above;
(c) drying the support after it has been so impregnated;
20 (d) sulphiding (or seleniding) the impregnated support at ambient or higher temperatures by exposing it to a gas stream containing a reactive sulphur (or selenide) compound such as hydrogen sulphide, carbonyl sulphide or carbon disulphide, or their selenide equivalents which has the effect of converting the metal and alkali salts to sulphides or selenides;

~ 6 1337069 (e) heating the impregnated support at an elevated temperature to drive off excess sulphur, or selenium so as to thereby form the bed in its pre-oxygenated form; and then, 5 (f) exposing the bed to a source of oxygen as, by way of example, to sulphur dioxide or nitrogen peroxide, whereby reactive oxygen becomes available within the bed and thereby create the bed in its oxygen-activated form.
This invention further comprises the production of elemental sulphur by the method of exposing a gas stream containing hydrogen sulphide to the oxygenated bed and then regenerating the bed. The bed is regenerated by first applying heat at a predetermined elevated temperature or temperatures (such as in the range of 250C to 600C) in the presence of a substantially non-reactive sweep gas. This will drive off water and elemental sulphur thus purging the bed of these substances. The regeneration process is then completed by exposure of such bed to an unreactive sweep gas containing an amount of oxygen as described above.
Optionally, oxygen as described above may also be provided during the initial purging step either aæ an alternative to subsequent treatment with an oxygen source, or in addition.

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- 7 - 1 3~7069 The amount of oxygen accompanying the sweep gas in the final step may range from a stoichiometric amount nec~ccAry to oxidize the sulphur compound to be treated and release elemental sulphur, up to a concentration of about 25%, although this is not 05 n~ceccArily limiting in all cases. In certain cases excess oxygen must be avoided to prevent damage to the bed.
This invention further comprises the method by which sulphur dioxide and nitrogen peroxide are first removed from a gas stream by permitting these compositions to be absorbed within a bed comprised of a microporous support which contains an alkali metal sulphide or selenide, and a sulphide or selenide of metals showing polyvalent and/or amphoteric character.
The bed, so impregnated, is then exposed to a stream of hydrogen sulphide whereby the absorbed sulphur dioxide and hydrogen sulphide are converted to water and elemental sulphur and the nitrogen peroxide is converted to nitric oxide. These products are then purged from the bed by heating the bed in the presence of a sweep gas, thus returning the bed to a condition whereby it is ready to repeat the cycle.
These and further features of the invention and its various aspects will be apparent from the description of the examples and test results set forth in the following.
Summarv of the Figures Figure 1 is a graph showing the effect of temperature on the rate of desorption of hydrogen sulphide from a series of sample catalytic beds which have been saturated with hydrogen sulphide.

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_ - 8 - 1 3 3 7 0 6 9 Figure 2 shows the capacity of a bed according to the invention to become loaded with hydrogen sulphide and sulphur dioxide as a function of pressure.
Characterization of the Catalyst within the Bed 05 The active catalyst within the bed that provides reactive oxygen is believed to be characterized by a chemical having as its constituents a complex containing the combination of an amphoteric and/or polyvalent metal (hereinafter referred to as the "metal"), an alkali metal, (hereinafter referred to as the "alkali"), sulphur or selenium and the capacity to retain an active oxygen-containing moiety that contains an available reactive oxygen group. This complex should preferably be formed within a microporous support having a relatively high surface area and a microporosity adapted to receive the sulphur or oxide compound to be decomposed.
Alumina is considered a preferred support because of its high surface area. Also, it is believed that alkali metal incorporated into the support to form the active complex will react with alumina to form an alkali aluminate and facilitate bonding of the active complex to the carrier. Alumina may thereby provide an etchable substrate upon which active sites may be more readily formed.
The process of solvent extraction using methylene chloride, when applied to an activated catalyst containing manganese and potassium sulphides on alumina (Alcoa #s-loo Trade Mark), showed the following extracted constituents:

9 ~ 3 3 7 0 6 ~

free manganous sulphide - 51% (by weight) free potassium sulphide - 18%

other constituents including 05 potassium aluminate and - 31%
potassium hydroxide An attempt to utilize methanol on the same catalyst produced inconclusive results as the constituents were apparently modified by the methanol as a solvent (perhaps by hydrolysis of the manganous sulphide) as was indicated by a change in colour of the solution from green to brown shortly after extraction.
It has been found that the catalyst is capable of decomposing a small portion of absorbed hydrogen sulphide without the addition of oxygen during the decomposition heating phase. The activity of the catalyst under such conditions, however, declines rapidly. It is believed that the catalyst is intrinsically capable of supplying small amounts of oxygen, but that this capacity is rapidly depleted.
This belief is supported by the observation that exposure of the catalyst to a reducing atmosphere causes catalytic decompositional activity to drop to virtually zero.

-- - lO - 1 337069 The provision of oxygen to the catalytic bed, either while decomposition is occurring or upon regeneration of the catalytic bed has been found necessary to preserve or restore the activity of the catalyst. Thus while oxygen may be 05 consumed in the decomposition cycle, it is readily restorable by exposure of the catalyst thereafter to a source of oxygen in either molecular or compound form.
The ability of a microporous support, impregnated with the components which form the active catalyst, to absorb certain oxygen compounds has a separate utility. A bed, prepared in accordance with the invention, will absorb not only molecular oxygen, but also sulphur dioxide and nitrogen peroxide. Both of these compounds are capable of producing the reactive oxygen which is characteristic of the invention.
This ability of the invention to become oxygen-activated with such compounds allows a catalytic bed, prepared in accordance with the invention, to be used to absorb such compounds from flue gas. The bed, once saturated, may then be purged of such compounds by exposure to hydrogen sulphide, followed by heating in the presence of a sweep gas. In the case of sulphur dioxide, this compound is decomposed into water and elemental sulphur. Thus a major pollutant in flue gas can be effectively removed from flue gas and converted to a valuable commodity.

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Preparation of the Catalytic Bed - Method 1 Catalytic beds were prepared by two alternate methods.
The first method commenced by dissolving a predetermined amount of the alkali sulphide (sodium or potassium) in water 05 sufficient to form the ultimate desired loading on the support and optionally boiling the solution. To this solution a molar equivalent amount of an amphoteric and/or polyvalent metal sulphide was added and the solution was boiled again until the volume was reduced to a point short of saturation. Then the support (generally in the form of Alcoa alumina spheres, #S-100) which had been dried by being heated to 250 C for 4 hours was added to the hot solution and mixed until all the solution was absorbed into the support. The partially prepared catalytic bed was then dried (using a nitrogen gas flow at 400C) and cooled.
The catalytic bed was then sulphided by exposure to a stream of 10% hydrogen sulphide in nitrogen or methane at ambient conditions until hydrogen sulphide was detected in the effluent and for at least one hour thereafter. It was then purged of excess sulphur by heating in a nitrogen gas flow at 400-500C for a period of 0.5 to 1.0 hours to drive off free sulphur.
The partially prepared catalytic bed can also be sulphided by exposure first to a stream of 10~ hydrogen sulphide in nitrogen or methane at 400-500C for 4 hours and then to a stream of nitrogen or methane at 400-500C to remove any excess sulphur. Some tests were run in which the conditioning gas was a 50/50 mixture of hydrogen sulphide and hydrogen and the active metal in the catalyst was manganese.

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~ 1 337069 This change in the nature of the conditioning gas considerably reduced its activity for the sample catalyst so prepared.
Preparation of the Catalyst - Method 2 A second method of preparing the catalytic bed was as 05 follows. A sulphate, chloride or nitrate of a polyvalent and/or amphoteric metal was dissolved in an aqueous solution.
The mixture was then heated to ensure rapid dissolution. (This, as above, is considered an optional step.) The solution was then impregnated on a previously dried alumina support (Alcoa S-100, 1/4 in. spheres) and the impregnated support dried.
A molar equivalent or greater amount of an alkali metal sulphide was then prepared in an aqueous solution and impregnated on the support. Again, heating was optionally employed to effect rapid dissolution.
The impregnated support was then heated to a temperature of 125C for a period of 2 hours in order to fix the active in-ingredients within the support. This was followed by a washing of the impregnated support with water until all available alkali sulphate, chloride or nitrate had been flushed from the support. The impregnated support was then dried at 125C.
It is believed that at this stage most of the sulphate, chloride or nitrate originally impregnated has become converted to a sulphide of the amphoteric and/or polyvalent metal. The available sulphate, chloride or nitrate salts of the alkali metal were washed out of the support because they t` ~

were not believed to contribute to the activity of the catalyst and were thought to reduce the availability of active sites within the support. The catalyst could be prepared without this step and still be capable of producing 05 some decomposition of hydrogen sulphide. However, it is believed that the catalyst would generally show reduced activity without this step.
A stoichiometric amount of the alkali metal sulphide was then prepared in an aqueous solution and impregnated on the carrier a second time. The impregnated support was finally dried at 125C, and sulphided and purged of excess sulphur as described in Method 1.
Preparation of the CatalYtic Bed - Further Alternate Methods The above process has been carried-out with a variety of amphoteric and/or polyvalent metals in the form of sulphates, chlorides or nitrates and, it is believed, may be carried-out with any soluble salts of such metals including zinc, iron, vanadium, copper, nickel, molybdenum, aluminum and manganese. It is believed that an active catalyst would be produced when these methods are carried out with all amphoteric and/or polyvalent metals. It is further believed that these methods would be effective in producing an active catalyst whether sulphide or selenide salts of all amphoteric and/or polyvalent metals are used. Where less soluble compounds are employed, it may be appropriate to employ a basic aqueous solution in order to facilitate dissolution. A sufficiently basic solution can be created by - 14 - 1 3370~9 adding alkali hydroxide to the solution of the amphoteric and/or polyvalent metal salt and boiling this mixture.
Method 2 described above has been followed using either sodium or potassium as the alkali element. It is 05 believed that lithium, rubidium or cesium sulphides may also be substituted for the elements sodium or potassium, and still form an active catalyst using either methods.
It is further believed that selenium may be substituted for the sulphur in the alkali sulphide and still produce an active catalyst.
Based on sample tests, a satisfactory st~n~rd of performance for the catalyst in terms of both absorptive and decomposing capacity can be obtained with an approximate 1:1 molar ratio between the metal and alkali components, and a similar 1:1 molar ratio where an alkali hydroxide is additionally employed.
Absorptive capacity for hydrogen sulphide is maximized for various metal sulphides at different levels of impregnation of the support. For example, this occurs between the 0.5% to 2.5% loading (by weight) range for a catalyst incorporating a zinc sulphide/sodium sulphide mixture deposited by Method 1 on the Alcoa carrier (S-100 spheres).
Preparation of the Catalytic Bed - Activation with Oxygen The bed may be activated in conjunction with the sulphiding steps by exposing it at ambient or higher temperatures to an unreactive gas containing hydrogen ~r~

sulphide, followed by heat treatment in an unreactive sweep gas at a temperature of 250C - 700C containing an amount of oxygen as referenced below. Alternately, after treatment with the sweep gas at elevated temperatures the bed may be exposed to oxygen at temperatures down to ambient conditions.
05 "Unreactive" is used here and throughout in the sense of a gas that does not substantially react in this system.
It is most desirable that the activating gas streams not contain appreciable amounts of compounds or elements, such as hydrogen, which will have a major reductive effect on the activity of the catalyst. It is also important that the catalyst be exposed by the conclusion of the conditioning process to sufficient oxygen to ensure that reactive oxygen will be available within the catalyst to render it activated.
The source of oxygen may be atmospheric oxygen, or nitrogen peroxide, but is preferably sulphur dioxide. All three of these sources have been found to produce, within the catalytic bed, the reactive oxygen which is a characteristic of the invention.
Sweeteninq, Decomosition, Purginq and Reactivation Procedures The procedure followed to verify and quantify the production of sulphur from hydrogen sulphide was as follows.

- 16 - l 3 3 7 0 6 9 A sample of a catalytic bed that had been purged of free sulphur and hydrogen sulphide by regenerating it at 400C
under an unreactive sweep gas (nitrogen or methane) and then activated by exposure to oxygen was weighed while placed in 05 a reaction tube. A measured volume of unreactive gas containing a known percentage of hydrogen sulphide was then passed over the catalyst bed at a specific temperature, usually ambient, to remove the hydrogen sulphide from the gas stream. This was designated as the "sweetening" cycle. The lo length of exposure was either that required to produce an indication of hydrogen sulphide "breakthrough" at the exit end (as measured by the blackening of st~n~rdized lead acetate paper, or other standard methods), or some lesser period of time. A run to breakthrough was said to have saturated the bed. A run carried to a point short of saturation was designated as a "partial run".
The catalytic bed in its tube was then weighed to determine either the saturation loading of the bed, or the partial loading of the bed, in terms of its absorption of hydrogen sulphide.
Throughout all experiments, the catalytic beds utilizing molecular sieves or alumina supports showed a capacity in the foregoing sweetening phase of maintaining the hydrogen sulphide level in the out-flowing stream below the measurable threshold vis, l part per million prior to breakthrough.
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The catalytic bed in its reaction tube was then put through the purging phase by exposing the bed to an unreactive sweep gas (nitrogen or methane) at a specific temperature above the vapourization point for elemental sulphur for a 05 period of time. The bed may then be reactivated by exposing it to a source of oxygen. This may be done, for example, by utilizing a sweep gas containing oxygen at levels of 0.01 to 25%. Oxygen is preferrably supplied in the form of sulphur dioxide or may be as nitrogen peroxide.
It has been found that with certain metals, such as manganese, that the catalytic bed deteriorates if e~rolsed to excessive levels of oxygen, e.g. over 10%. This may, it is believed, be due to the formation of a sulphate. The catalyst in such a case was restored to activity on re-exposure to hydrogen sulphide. However, it is believed that the concentration of oxygen should preferably be limited in order to avoid such deleterious effects.
The sweep gas exiting the catalytic bed was caused to pass through a portion of the reaction tube that was maintained at room temperature. During this process, when carried out with the bed at temperatures over about 250C -300&, sulphur consistently condensed on the inside walls of a cooler, exit portion of the reaction tube in a condensation zone. Sample tests with glasswool placed downstream of such deposits indicated that further sulphur could not be collected by condensation from the cooled exiting gas stream beyond the condensation zone.
A further procedure followed in some experiments was 05 to collect the exiting sweep gas during regeneration step and then determine its hydrogen sulphide concentrations by gas chromotography. As further discussed below, little or no hydrogen sulphide was detected in the regeneration phase when the catalyst bed was only partially loaded with hydrogen sulphide, well below the saturation level for the bed. For higher loadings and approaching saturation, much more hydrogen sulphide was detected in the regeneration stage of treatment.
After sulphur ceased to be forming further within the cooler portion of the reaction tube, the tube and bed were reweighed. Comparisons of this weight with the weight of the tube following sweetening showed that virtually all of the sulphur remained in the system, up to this point. Then heat was applied to the outside portion of the reaction tube where sulphur had deposited and the sweep gas flow was maintained.
This procedure was continued until all of the sulphur in the reaction tube had been vapourized and carried out of the tube.
The reaction tube and bed were then reweighed.
The catalyst bed, for purposes of experimental certainty, was then put through a super-purging phase by performing the previous procedure at 400-500C for 1-2 hours.
This step was shown through tests at higher temperatures to be -capable of completely purging the catalyst bed of remaining traces of free sulphur and residual hydrogen sulphide.
The inclusion of small amounts of oxygen in the sweep gas during the super-purging phase was not found to be 05 essential if it had been previously present as part of the earlier treatment. Apparently, if sufficient oxygen is available during the normal purging phase, then the catalyst is reactivated. However, no deleterious effects occurred where oxygen was present on the super-purging phase as well.
If insufficient oxygen was present during the purging or super-purging phases, then oxygen should be supplied to the bed as a further step, which may be carried out at room temperature.
While oxygen may be supplied to the bed in its molecular form, or in a compound such as sulphur dioxide or nitrogen peroxide. Sulphur dioxide has been found to produce a much higher deposition of reactive oxygen within the catalyst. The use of sulphur dioxide also increases the absorptive capacity of the bed with respect to hydrogen sulphide.
The exposure of alumina to sulphur dioxide would normally be expected to result in the production of aluminum sulphite. If oxygen is present, as well, then aluminum sulphate will form. Where, however, alumina has been treated by the deposition therein of the combination of sulphide or selenide salts of amphoteric or polyvalent metals combined with " .
. ~ ., sulphite or selenide salts of alkali metals, the tendency of the alumina to form aluminum sulphite or sulphate is believed to be significantly reduced.
It has been found that when sulphur dioxide is used as 05 the source for oxygen, it is relatively tenaciously contained within alumina-type supports. This enables an activated bed to be prepared in one location, and then transported to another. Similarly where the bed is only partially saturated with hydrogen sulphide in the sweetening cycle, the bed material is readily transportable.
These features will allow the establishment of centralized regeneration facilities for a number of sweetening units placed in the field.
From the foregoing procedures calculations were made to determine the extent to which the hydrogen sulphide was converted to sulphur. The quantity of hydrogen sulphide absorbed in the catalyst bed was calculated based both on the gas flow rate, and on the gain in weight of the bed and tube during the sweetening phase. The quantity of sulphur produced was obtained from the heat-vaporization procedure. The actual quantity of hydrogen sulphide decomposed was also determined by the difference between the volume of hydrogen sulphide absorbed by the catalyst, and the volume of hydrogen sulphide collected by a gas bag during the regeneration. Of these methods, the mass of sulphur vaporized off the interior of the reaction tube was taken as the more reliable measure of the minimum decomposition that had occurred.

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- 20a -Absorption of Sulphur Dioxide The procedure of utilizing the bed first to absorb hydrogen sulphide followed by reactivation with sulphur dioxide may be reversed or shifted in order. Thus, where it 05 is desired to remove sulphur dioxide from a gas stream the bed is first purged of sulphur dioxide by exposure to hydrogen sulphide, then purged of sulphur by heating in the presence of a sweep gas. So prepared, the bed will then readily absorb sulphur dioxide to the limit of saturation. Once the bed has been saturated with sulphur dioxide, it may be again exposed to hydrogen sulphide .

-This process has utility in the removal of sulphur dioxide from flue gases.
Absorption of Nitrogen Peroxide The source of oxygen may also be nitrogen peroxide.
05 This is a component often found in the products of combustion and in flue gases.
When nitrogen peroxide is used as the source of oxygen, subsequent exposure of the bed to hydrogen sulphide results in the production of elemental sulphur, water and nitric oxide - NO. When the catalyst is purged of sulphur by heating, the nitric oxide evolves. This nitric oxide can then be trapped downstream, after air-oxidation to nitrogen peroxide and then used for other chemical reactions.
The advantage of this cycle is that the bed can be employed to first absorb the nitrogen peroxide, separating it from a flue gas stream for subsequent recovery.

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- 22 - ~ 337~69 Desorption Runs - Effects of Physical Absorption From the results of the tests performed, it was deter-mined that hydrogen sulphide was believed to be both physically and chemically absorbed within alumina based 05 catalysts. Tests on a blank alumina support, containing no active ingredients, indicated that virtually all absorbed hydrogen sulphide could be driven out of such a support by heating it to 350C under a sweep gas for a period of time of 90 minutes. Supports that had been impregnated with ingredients to form the catalyst showed a tendency not to have released as much hydrogen sulphide at that temperature as did the blank support.
Figure 1 shows this effect in which a blank Alcoa (S-100) alumina support is compared with catalysts prepared by Method 1 with Zinc and Potassium sulphide; Zinc, Copper and Potassium sulphides, and Copper and Potassium sulphides all on the same type of S-100 support. All beds were loaded to saturation and then treated in the sweetening phase for 90 minutes at various temperatures. Figure 1 shows the percentage of the hydrogen sulphide evolved, as a function of temperature after heating for 90 minutes at various temperatures.
Table 1 summarizes the data depicted in Figure 1 and adds the accumulated percent decomposition obtained both after the 90 minute heating at a constant temperature and after the final regeneration at 400C. These percentages are based in both cases on conversion of sulphur, being the mass of sulphur vaporized divided by the mass of sulphur available in the - quantity of hydrogen sulphide originally absorbed.

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- 23 - 1 33~069 Table 1 Effect of Heating at Various Temperature on Hydrogen Sulphide Desorption and Decomposition for Saturated Catalyst/Beds 05 Catalyst/Bed HeatOng Temp % Desorption % Sulphur Conversion ( C) H S After Total after After ~eating Heating Regeneration Blank Crushed Alcoa O
Support #S-10018 C 35 -- --loo 73 --300 93 __ __ 325 94 __ __ Zinc -Sodium 18 42 -- 1.6 Sulphides 100 70 -- 7.8 150 80 -- 10.3 200 83 -- 17.2 250 90 1.6 10.2 300 87 3.3 10.2 350 88 7.0 7.5 400 93 6.1 6.1 Zinc Copper - 18 n/a -- 2.6 Sodium 68 -- 14.7 Sulphides 200 79 -- 9.8 300 81 3.2 10.8 350 94 5.3 6.3 400 96 3.2 3.2 Copper-Sodium 18 42.1 -- 8.2 Sulphides 350 95.7 1.1 1.5 (Heating Time: 90 minutes) ~., ~ 1 337069 Partial Runs The foregoing data on saturated catalyst beds give a clear indication that decomposition is occurring by the showing of elemental sulphur that is produced. However, the 05 decomposition effect is being masked by the large proportion of hydrogen sulphide that is being physically absorbed, and then being desorbed without decomposing. The masking effect of physically absorbed hydrogen sulphide can be largely eliminated by exposing the catalyst to hydrogen sulphide streams for periods of time less than that necessary to saturate the bed. These are called "partial runs".
In such partial runs, the amount of hydrogen sulphide evolved on regeneration was substantially reduced. Correspondingly, higher percentage figures for the amount of available sulphur in the hydrogen sulphide converted to elemental sulphur were obtained.
The catalyst, when used in association with microporous supports such as alumina or zeolite, rapidly absorbs hydrogen sulphide. It may be that the rapidity with which the hydrogen sulphide is absorbed permits the catalytic bed, at suitable flow rates, to saturate progressively when exposed to a sour gas stream. If the sweetening phase is terminated with only a portion of the bed exposed (and saturated) with hydrogen sulphide, then, as heat is applied to the bed in the presence of a sweep gas absorbed hydrogen sulphide that may be desorbed is swept into a region of the bed containing unexposed catalyst. Consequently, a bed that A

-is partially loaded to saturation along only a portion of its length would be capable, in the separation phase, it is believed, of exposing virtually all of the hydrogen sulphide to chemical-absorption leading to decomposition.
05 Thus, on whatever basis, it has been found that with appropriately chosen partial loadings, it is possible to obtain virtually 100% dissociation.
Tested Catalyst Variants The dissociative capacity of different catalyst formulations were tested and some of the results obtained were as set out in Tables 2 and 3.

~TATYST LOADING % SULPHUR CONV~K' (including method (gms/100 gms (cumuOative, at of preparation) and as a % 400 C) of saturation) Zn-K-lC-l 0.6(20%) >90%
Zn-K-2W-1 0.7(23%) >80%
Cu-K-lW-2 1.4(100%) >70%
Mn-K-lC-l 0.6(20%) >90%
(Catalyst designation code:
Zn - K - lC
main amphoteric alkali carrier: method of or polyvalent metal 1 - Alcoa preparation metal 2 - ICI 1 - method 1 c - crushed 2 - method 2 using w - whole a sulphate.) - 26 - ~ 3 3 7 0 6 9 The data in Table 2 provides quantitative figures on the extent of decomposition of hydrogen sulphide obtained, stated in terms of the percent conversion to sulphur.
Table 3 lists combinations of further ingredients all 05 found to produce nonquantified but definite amounts of elemental sulphur upon the consecutive exposure of the catalytic bed to a 10% hydrogen sulphide/90% nitrogen gas stream at ambient temperature 18C), followed by regeneration of the catalyst at temperatures ranging from 350-400C as previously described. All runs were carried out using as a support the Alcoa alumina carrier No. S-100. All of the samples listed in Table 3 were prepared from sulphides in accordance with the procedure of Method 1.
The column entitled "Absorptive Capacity" indicates the percentage ratio of mass of sulphur absorbed to the mass of catalyst, at the point where the catalyst bed ceased to fully absorb further hydrogen sulphide (as tested by the darkening of lead acetate paper at the exit).

Metal Alkali Elemental Absorptive Capacity Metal Sulphur (% sulphur loaded 05 Detected per mass of catalyst) Zinc Sodium Yes 2.4 Zinc Potassium Yes 1.4 Iron Sodium Yes 2.4 Vanadium Sodium Yes 2.3 Copper (I) Sodium Yes 2.9 Copper (II) Sodium Yes 2.0 Copper (II) 2 Sodium Yes 2.4 Copper (II) Potassium Yes 2.2 Nickel Sodium Yes 2.9 Molybdenum Sodium Yes 2.3 Aluminum Sodium Yes 2.7 Manganese Sodium Yes 2.8 Manganese Potassium Yes 2.3 Cobalt Sodium Yes n/a Tested Catalyst Variants - Mixed Catalysts A number of combined catalysts incorporating two or three amphoteric and/or polyvalent metals have been tested.
Table 4 sets out the absorptive capacity at room temperature for all such catalysts based on the alumina support, Alcoa No.
S-100. In all cases the catalyst was prepared by Method 1 using a sulphide of the metal as the initial salt. All components were incorporated into the support in equal molar ratios.

. .~. ~,, ., Metal Components Alkali Component Absorptive Capacity (gms sulphur equivalent from H2S in 100 gms catalyst) Iron & Zinc Sodium Sulphide 2.3 Iron, Copper & Sodium sulphide and Zinc Sodium hydroxide 2.2 Manganese & Zinc Sodium sulphide and Sodium hydroxide 2.0 Manganese & Zinc Sodium sulphide 2.3 Manganese & Nickel Potassium sulphide 1.5 Manganese &
Molybdenum Potassium sulphide 1.7 Iron & Zinc Potassium sulphide 1.2 In all of the cases listed in Table 4, sulphur was observed to be evolved when the catalysts were regenerated at a temperature of 400C.
Description of Examples Using Sulphur Dioxide A two-to-one molar ratio of sodium sulphide and zinc sulphide was deposited on S-100 Alcoa Alumina Spheres. The amount of such components deposited was set, for two different samples, at 1% and 2% by weight of the final loaded support.
One hundred grams each of the two classes of catalyzed support, along with pure, crushed S-100 spheres were then progressively loaded with sulphur dioxide at room temperature by exposure to a stream of 18% concentration by volume of S0 in nitrogen; and then exposed to a stream of methane containing X

- 29 - 1 337~69 10% by volume of hydrogen sulphide. The amounts of sulphur-equiva-lent absorbed and then converted to sulphur are shown in Table 5 where a comparison to a blank alumina support is also provided.

05 S0 & H S Loading and Regeneration Data ~or A~ 0 , 1% and 2~ - 2NaN S.ZnS
un~e~ Saturation conditions Run S0 H S Total S % Con-No. BedLo2ading Loading Loading version Comments 1. Al 0 3.3 5.3 8.6 77 (crushed)

2. Al 0 3.1 5.3 8.4 72 (crushed)

3. Al 0 3.1 5.2 8.3 66 (c~ushed)

4. Al 0 3.4 5.1 8.5 75 (c~ushed)

5. 1% Catalyst 4.2 7.7 11.9 82 The catalyst

6. 1% Catalyst 4.7 6.9 11.6 82 shows higher

7. 1% Catalyst 4.6 7.3 11.9 79 absorption and

8. 1% Catalyst 4.6 7.3 11.9 79 conversion

9. 1% Catalyst 4.6 7.4 12.0 79 capacity

10. 2% Catalyst 4.4 7.9 12.3 83 2% catalyst shows

11. 2% Catalyst 4.4 7.3 11.7 79 similar behaviour

12. 2% Catalyst 4.6 7.2 11.8 78 compared to the

13. 2% Catalyst 4.3 6.5 10.8 80 1% catalyst S2 and H S loading figures are in grams of Sulphur per 100 g of catalyst.

_ 30 _ 1 3 3 7 0 6 9 In order to determine if the absorptive capacity of the catalyzed supports changed over time, the 1% loaded and blank alumina samples of Table 5 were saturated by exposure to consecutive streams of 1.9% sulphur dioxide, and 6.7% oxygen, 05 both in methane, at room temperature, for one hour each.
These samples were then allowed to stand at room temperature for 70 hours in sealed moisture-proof containers.

Loading and Regeneration Data for the S02 Saturated Beds After Soaking for 70 hrs at Room Temperature Run S0 H S Total No. Bed Loading Loading S Loading Conversion 1. A123 2.7 4.2 6.9 68 2. 1% catalyst 4.8 6.8 11.6 80 Table 6 shows the data obtained when these aged samples were exposed to hydrogen sulphide on the same basis as previously. From Table 6 it is apparent that the bare alumina absorbed a smaller quantity of sulphur dioxide than in the earlier tests, after exposure to this aging test, but the catalyzed beds was unaffected.
During the sweetening runs with beds activated with S02 it was found that some sulphur dioxide was evolving and finding its way into the effluent gas. As much as 28~ of the sulphur dioxide would become desorbed at 150 psi. This is believed to be due to the highly exothermic character of the reaction of hydrogen sulphide and sulphur dioxide.
To reduce this effect, tests were run with the beds only partially saturated with S02 (i.e.: to 75% of capacity).
05 Utilizing beds of catalyst constituted by 1% by weight of 2 sodium sulphide/zinc sulphide on S-100 Alcoa spheres that had been only partially saturated in this manner, a series of sweetening and conversion cycles were run at varying pressures. The results are set out in Table 7.

H2S Loading As A Function of Pressure For The Partially S02-Loaded Beds RunS0 H S Total S %
No. Pressure Loading Loading Loading Conversion 1.150 psi 5.9 10.4 16.3 85 2.150 psi 6.0 10.4 16.4 88 3.80 psi 3.9 8.4 12.3 80 4.80 psi 3.9 7.7 11.6 81 5.40 psi 3.6 6.8 10.4 77 6.40 psi 3.8 6.6 10.4 77 In the runs depicted in Table 7, no sulphur dioxide z5 was evolved until just before break-through of the hydrogen sulphide occurred, and even then only trace amounts were detected.
Table 7 shows sulphur conversion ratios that are on the same order as those of Table 5. Further, the increased ~, - 32 - ~ 3 3 7 0 6 9 absorptive capacity of the catalyzed support under pressure is also shown.
The actual dependence of absorptive capacity under a range of pressures was also determined using a 1% loading of 05 2Na2S/ZnS deposited on S-100 supports that were progressively saturated with sulphur dioxide and then saturated with hydrogen sulphide, both to the point of breakthrough. The results are shown in Table 8. These results are reproduced graphically in Figure 2.

Loading As A Function of Pressure for the Catalyst 2Na2S/ZnS

Run SO H S
No Pressure Loading Loading Total S Loading (as % S) (as ~ S) 1. 14.7 psig 4.6 7.3 11.9 2. 54.7 psig 5.0 8.1 13.1 3. 94.7 psig 5.9 9.2 15.1 4. 164.7 psig 10.3 9.6 19.9 Since the reaction between hydrogen sulphide and sulphur dioxide requires twice the amount of hydrogen sulphide to be stoichiometric, it is apparent from Table 8 that above 100 psi, the capacity of the catalyzed support to absorb sulphur dioxide outstrips that of hydrogen sulphide.
Consequently, at higher pressures, it is preferable that the catalyzed support be only partially saturated with sulphur -~ 33 ~ 1 3370b9 dioxide. This will avoid the evolution of excess sulphur dioxide while still providing a stoichiometrically sufficient amount of sulphur dioxide to react with the hydrogen sulphide that can be absorbed.
05 Throughout the foregoing tests, during the sulphur purging stage, tests for the presence of hydrogen sulphide in the sweep gas were made. In the process described which relied on the depositing of molecular oxygen within the catalyst, quantities of hydrogen sulphide were released at this stage. By the process described herein of activating the catalyst with sulphur dioxide, the release of hydrogen sulphide from the catalyst can be greatly reduced.
Supports The principal support used in testing has been alumina in the form of Alcoa 1/4 or 3/4 inch spheres (#S-100). Other supports tested for absorptive capacity include alumina in the form of Norton 5/16" rings (#6573), Norton spheres (#6576); CIL Prox-Svers non-uniform spheres, Davison Chemical molecular sieves (type 13x, 4-8 mesh beads), silica and char. The Alcoa support was chosen as the preferred carrier due to its high absorptive capacity, which was due, in turn, to its large surface area (325m /gm).
The Alcoa support referenced is essentially alumina that is reported as being in the gamma and amorphous form. It is not believed that the type of crystalline form in which the alumina may be found is of significance to the dissociative capacity of the catalyst.

, .

Activity has been found where there is aluminum present in the support. The presence of aluminum in the support is relevant in that alumina will invariably be formed.
When preparing the catalyst, the alkali metal will attack the 05 alumina and form alkali aluminate and species containing available reactive oxygen. Thus the aluminum-containing supports inherently are capable of providing active centres necessary to support the activity of the catalyst. Such supports also provide an etchable base upon which actively catalytic sites are thought to be more likely to form.
Supports were tested for decomposition activity when aluminum was not present. A distinct but non-quantified showing of production of elemental sulphur occurred on repeated cycles of exposure of an oxygen activated catalyst formed on a silica support, to a continuous stream of 10%
hydrogen sulphide. This was based upon manganese and sodium as the active metal and alkali respectively. Due to the reduced surface area of this latter carrier, only trace amounts of sulphur were produced, and no quantitative measurements of decomposition were made.
However, this test demonstrated that it is not essential that the support upon which the catalyst is based contain aluminum.
The capacity of the support to fully absorb hydrogen sulphide and/or other sulphur compounds is an important feature when it is desired to remove all significant traces of such compounds from a gas stream. This characteristic is believed to be dominated by the support itself. When the ~ 35 ~ 1 337069 production of sulphur is the primary objective, the efficiency of absorption by the carrier is less critical. In such cases supports may be used that do not effect 100% absorption of hydrogen sulphide prior to saturation.
05 Recyclability of the Catalyst The prepared catalysts were run through at least 4 cycles of absorption and regeneration before quantified tests were carried out on them. These initial cycles were found appropriate to stabilize the catalyst and obtain relatively consistent results in subsequent tests. Generally, the activity of the catalyst in terms of its decomposing capacity increased following these preliminary recyclings. The presence of oxygen at least in small amounts during or after the purging phase of the process was found to be essential to restore the activity of the catalyst. It is believed that the catalyst oxidizes the non-sulphur components of the absorbed compounds using internally available oxygen. In the case of hydrogen sulphide, this results in the release of water. Oxygen is then required to replenish the oxygen so consumed.
No significant decline or loss of activity in dissociative capacity of the catalyst has been found despite a number of consecutive absorption and regeneration cycles so long as replacement oxygen is available. The absorptive capacity of the catalyst has been shown to remain relatively unchanged through at least 30-40 cycles of absorption and regeneration.

Effects of Carbon Dioxide. Water and Heavy Hydrocarbons and Decomposition on Hydrogen Sulphide Absorption When carbon dioxide is present in the gas stream it does not substantially affect the capacity of the catalytic 05 bed to absorb hydrogen sulphide, but is itself absorbed. The presence of absorbed carbon dioxide within the bed does not significantly affect the decomposition of hydrogen sulphide.
When water is present in or exposed to the catalytic bed as a vapour component in a gas stream, the performance of the alumina-supported catalyst in terms of absorptive capacity is somewhat enhanced. Water has not been found, however, to have a significant effect on the decomposing capacity of the catalyst.
When used to remove hydrogen sulphide from gas streams cont~;n;ng high boiling point hydrocarbons, contamination of the catalyst can occur. Prior scrubbing of the gas stream has been found necessary to reduce the effects of this problem.
Pressure Effects on Absorptive Ca~acity for Hydrogen Sulphide The absorptive capacity of the catalyst (in terms of the ratio of the mass of hydrogen sulphide removed in the absorption stage to the mass of the catalyst) is relatively insensitive to the concentration of hydrogen sulphide in the gas stream for concentrations of hydrogen sulphide up to 10%. It rises, however, approximately linearly with total pressure, up to at least 500 psig.
At modest flow rates, the rate of removal of hydrogen sulphide by absorption in the case of alumina carriers is relatively high, up to the point where the catalyst bed has been nearly totally saturated with hydrogen sulphide at ambient temperature and pressure.

_ 37 _ ~ 33 7~69 Some tests were done with a 3 minute residence time.
Other tests were done with a 0.7 minute residence time. In both cases Alcoa alumina carriers impregnated with the necessary ingredients to form the catalyst were capable, 05 before saturation, of removing virtually 100~ of the hydrogen sulphide from the gas stream. The level of hydrogen sulphide prior to breakthrough was below the threshold of measurability, in both cases being below 1 ppm.
Throughout the laboratory tests, nitrogen or methane containing small amounts of oxygen was used in most cases to reactive the catalyst after the sulphur was driven-off using oxygen-free nitrogen or methane as the sweep gas.
In some tests effected using a source of sour natural gas, the hydrogen sulphide absorptive capacity of sample catalytic beds (based on the Alcoa carrier) was similar to that obtained with the nitrogen as the background gas. While quantitative measurements of decomposing capacity were not made in these latter tests, visual examination of the catalyst bed after exposure to sour natural gas and before regeneration showed clear deposits of yellow sulphur. From this it is concluded that the substitution of natural gas for nitrogen or pure methane as the background gas and as the sweep gas does not significantly decrease the absorptive or dissociative capacity of the catalyst.

.. .

Decomposition of Other Sul~hur Compounds While tests have been carried out mainly on hydrogen sulphide as the decomposed sulphide, it is believed that the catalyst will be active in decomposing carbonyl 05 sulphide, carbon disulphide, mono and dialkyl sulphides, alkyl-type disulphides and thiophene. It would also be suitable for removing all of the foregoing from a mixture of more complex natural gas components in gaseous or liquid phase, such as from butane or propane.
Absorption of Oxygen Compounds Tests based on the activation of a 2Na2S/ZnS form of calatyst deposited in S-100 Alcoa spheres (at 1% loading, by weight) show a capacity for such a bed to absorb up to 6% by weight of sulphur dioxide, 9.1% by weight of nitrogen per oxide and 6% of carbon dioxide, simultaneously. The gas stream used for this test contained 10-12% of CO2; 4-6% of 2;
1000-2000 ppm of SO2 and 100-400 ppm of NO2. These ratios are typical for a flue gas. The absorption capacities for each of these components do not appear to be substantially cross-related.
When a combination bed of oxygen-activated catalyst, con-taining all three of the above components was treated with hydrogen sulphide, the oxides of sulphur and nitrogen reacted with the hydrogen sulphide to produce sulphur and water. Then, on heating, the bed was purged of sulphur, nitric oxide and carbon dioxide.

. ~.~

- 39 _ 1 337069 Conclusion The foregoing disclosure has identified various features of the invention. These and further aspects of the invention, in its most general and more specific senses, are 05 now described and defined in the claims which follow.

Claims (21)

The embodiments of the invention in which an exclusive privilege is claimed are as follows:

1. A method of decomposing sulphur-containing compounds from a gas stream containing such compounds to produce elemental sulphur including:
(1) contacting said gas, at a temperature below the vapourization point of sulphur, with a catalyst composition deposited on a catalytic support, said composition comprising a mixture of at least two salts, (a) the first of said salts comprising a sulphide or selenide of at least one metal selected from the group of amphoteric or polyvalent metals, or mixtures thereof, (b) the second of said salts being a sulphide or selenide of an alkali metal, and (c) there being present, immobilized within said support, at least one component capable of providing or generating reactive oxygen whereby said reactive oxygen is reactable with said non-sulphur component of the said compound to form sulphur followed by the step of, (2) heating said catalyst in the presence of an sweep gas so as to drive-off elemental sulphur as a vapour, (3) exposing said catalyst to sulphur dioxide or nitrogen peroxide so as to recondition it for reuse.

2. A method as in claim 1 wherein said support is selected from the group of supports comprised by alumina, zeolites, molecular sieves, silica and char.

3. A method as in claim 1 wherein said support is adapted to absorb alkyl sulphides or hydrogen sulphide.

4. A method as in claim 1 wherein one of the salts is a sulphide.

5. A method as in claim 1 wherein both of said salts are sulphides.

6. A method as in claim 1 wherein said amphoteric or polyvalent metal is selected from the group consisting of zinc, manganese, iron, copper, cobalt, aluminum, vanadium, molybdenum, tin and nickel, and mixtures thereof.

7. A method as in claims 1, 2 or 3 wherein the alkali metal is selected from the group consisting of lithium, sodium, potassium, rubindium and cesium.

8. A method as in claims 4, 5 or 6 wherein the alkali metal is selected from the group consisting of lithium, sodium, potassium, rubidium and cesium.

9. In a catalytic composition deposited on a catalytic support suitable for use for treating a sulphur-containing composition having at least one sulphur compound containing a non-sulphur component, the improvement wherein said composition is a composition obtained by the method of (1) impregnating said support with a mixture of at least two salts, (a) one of said salts comprising at least one sulphide or selenide of at least one metal selected from the group of amphoteric or polyvalent metals, or mixtures thereof, (b) the other of said salts being at least one sulphide or selenide of an alkali metal, (2) drying said support once so treated, (3) then conditioning said composition by exposure of said support to a stream of hydrogen-sulphide, (4) removing excess sulphur by heating said support in the presence of a sweep gas, and (5) exposing said support to an amount of sulphur dioxide or nitrogen peroxide in order to conclude the conditioning, there being thereby present reactive oxygen which is reactable with said non-sulphur component of said sulphur-containing compound to form sulphur.

10. A method of sweetening a sour natural gas stream and producing sulphur therefrom comprising:
(1) providing a stream of a sour natural gas, containing at least one sulphur compound having a non-sulphur component;
(2) exposing said stream at a temperature below the vapourization point of sulphur to an active catalytic composition deposited on a catalytic support wherein said composition is obtained by treating said support with a mixture of at least two salts, (a) one of said salts comprising at least one sulphide or selenide of at least one metal selected from the group of amphoteric or polyvalent metals, or mixtures thereof, (b) the other of said salts being at least one sulphide or selenide of an alkali metal (c) drying said support, and further treating said support by, (d) conditioning said composition by exposure of said support to a stream of hydrogen-sulphide, then (e) removing excess sulphur by heating said support in the presence of a sweep gas at a temperature above the vapourization point of sulphur, and (f) exposing said support to an amount of sulphur dioxide or nitrogen peroxide in order to conclude the conditioning, there thereby being present reactive oxygen whereby said reactive oxygen is reactable with a non-sulphur component of a sulphur-containing compound to form sulphur.
(3) heating said catalytic composition at a temperature above the vapourization point of sulphur in the presence of a sweep gas so as to produce elemental sulphur.

11. A method of removing sulphur dioxide from a gas stream comprising:
(1) providing a stream of gas, containing sulphur dioxide;
(2) providing a catalytic composition deposited on a microporous support adapted to absorb sulphur dioxide wherein said composition contains a mixture of at least two salts, (a) one of said salts comprising at least one sulphide or selenide of at least one metal selected from the group of amphoteric or polyvalent metals, or mixtures thereof, (b) the other of said salts being at least one sulphide or selenide of an alkali metal, (c) said composition having been treated by exposure to a reducing gas so as to substantially remove any reactive oxygen deposited therein, (3) exposing said flue gas to said catalytic composition so prepared, so as to permit the absorption of sulphur dioxide;
(4) converting a portion of said sulphur dioxide within said composition to sulphur.
(5) purging said composition of sulphur by exposing it to a sweep gas at a temperature above the vapourization point of sulphur.

12. A method as in claim 11 wherein said support is selected from the group of supports composed by alumina, zeolites, molecular sieves, silica and char.

13. A method as in claim 11 wherein said support is adapted to absorb alkyl sulphides or hydrogen sulphide.

14. A method as in claim 11 wherein one of the salts is a sulphide.

15. A method as in claim 11 wherein both of said salts are sulphides.

16. A method as in claim 11 wherein said amphoteric or polyvalent metal is selected from the group consisting of zinc, manganese, iron, copper, cobalt, aluminum, vanadium, molybdenum, tin and nickel, and mixtures thereof.

17. A method as in claims 11, 12 or 13 wherein the alkali metal is selected from the group consisting of lithium, potassium, sodium, cesium and rubidium.

18. A method as in claims 14, 15 or 16 wherein the alkali metal is selected from the group consisting of lithium, potassium, sodium, cesium and rubidium.

19. A method of decomposing sulphur-containing compounds from a gas stream containing such compounds to produce elemental sulphur including:
(1) contacting said gas, at a temperature below the vapourization point of sulphur, with sulphur dioxide deposited on a microporous catalytic support, said support comprising a mixture of at least two salts, (a) the first of said salts comprising a sulphide or selenide of at least one metal selected from the group of amphoteric or polyvalent metals, or mixtures thereof, (b) the second of said salts being a sulphide or selenide of an alkali metal, and there being present, immobilized within said support, at least one component capable of providing or generating reactive oxygen whereby said reactive oxygen is reactable with said non-sulphur component of the said compound to form sulphur;
followed by the step of, (2) heating said catalyst in the presence of an unreactive sweep gas so as to drive-off elemental sulphur as a vapour.
(3) exposing said microporous catalyst support to sulphur dioxide or nitrogen peroxide so as to recondition it for reuse.

20. A method of sweetening a sour natural gas stream comprising:
(1) providing a stream of a sour natural gas, containing at least one sulfur compound having a non-sulphur component;
(2) exposing said stream at a temperature below the vapourization point of sulphur to sulphur dioxide or nitrogen peroxide deposited on a catalytic support, said support comprising a mixture of at least two salts, (a) the first of said salts comprising a sulphide or selenide of at least one metal selected from the group of amphoteric or polyvalent metals, or mixtures thereof, (b) the second of said salts being a sulphide or selenide of an alkali metal, and (c) there being present, immobilized within said support, at least one component capable of providing or generating reactive oxygen whereby said reactive oxygen is reactable with said non-sulphur component of the said compound to form sulphur followed by the step of, (3) heating said catalytic composition at a temperature above the vapourization point of sulphur in the presence of a sweep gas so as to produce elemental sulphur.

21. A method of removing sulphur dioxide from a gas stream as in claim 11 wherein the step of converting a portion of said sulphur dioxide within said support to sulphur os effected by exposing it to a reducing gas.